When renovating buildings or making a metro station below the ground, such constructions are not easily covered during the construction period. Thus, covering facilities have to be very strong to have the required wide, free span and are therefore made to be of a more permanent character in order to be able to bear this wide free span and withstand the wind forces acting on the facility during high winds. Furthermore, in the northern countries, such constructions have to withstand the heavy load from snowfall.
Furthermore, the assembly of such temporary cover or production facility over an existing building or future underground station is also very difficult, as the cranes for lifting the covering structures cannot stand underneath due to the building to be renovated or the fact that there is a hole in the ground where the descent to the station is to be built. Therefore, very large and thus very expensive cranes are required for mounting such cover or production facility. And this adds substantial costs to the process of renovating a building or constructing an underground station.